core/packages/runtime-core/__tests__/rendererOptimizedMode.spec.ts

import {
  Fragment,
  type FunctionalComponent,
  type SetupContext,
  Teleport,
  type TestElement,
  type VNode,
  createApp,
  createBlock,
  createCommentVNode,
  createTextVNode,
  createVNode,
  defineComponent,
  h,
  serializeInner as inner,
  nextTick,
  nodeOps,
  onBeforeUnmount,
  onUnmounted,
  openBlock,
  ref,
  render,
  renderList,
  renderSlot,
  serialize,
  withCtx,
} from '@vue/runtime-test'
import { PatchFlags, SlotFlags } from '@vue/shared'
import { SuspenseImpl } from '../src/components/Suspense'

describe('renderer: optimized mode', () => {
  let root: TestElement
  let block: VNode | null = null

  beforeEach(() => {
    root = nodeOps.createElement('div')
    block = null
  })

  const renderWithBlock = (renderChildren: () => VNode[]) => {
    render(
      (openBlock(), (block = createBlock('div', null, renderChildren()))),
      root,
    )
  }

  test('basic use of block', () => {
    render((openBlock(), (block = createBlock('p', null, 'foo'))), root)

    expect(block.dynamicChildren!.length).toBe(0)
    expect(inner(root)).toBe('<p>foo</p>')
  })

  test('block can appear anywhere in the vdom tree', () => {
    render(
      h('div', (openBlock(), (block = createBlock('p', null, 'foo')))),
      root,
    )

    expect(block.dynamicChildren!.length).toBe(0)
    expect(inner(root)).toBe('<div><p>foo</p></div>')
  })

  test('block should collect dynamic vnodes', () => {
    renderWithBlock(() => [
      createVNode('p', null, 'foo', PatchFlags.TEXT),
      createVNode('i'),
    ])

    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p>foo</p>',
    )
  })

  test('block can disable tracking', () => {
    render(
      // disable tracking
      (openBlock(true),
      (block = createBlock('div', null, [
        createVNode('p', null, 'foo', PatchFlags.TEXT),
      ]))),
      root,
    )

    expect(block.dynamicChildren!.length).toBe(0)
  })

  test('block as dynamic children', () => {
    renderWithBlock(() => [
      (openBlock(), createBlock('div', { key: 0 }, [h('p')])),
    ])

    expect(block!.dynamicChildren!.length).toBe(1)
    expect(block!.dynamicChildren![0].dynamicChildren!.length).toBe(0)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<div><p></p></div>',
    )

    renderWithBlock(() => [
      (openBlock(), createBlock('div', { key: 1 }, [h('i')])),
    ])

    expect(block!.dynamicChildren!.length).toBe(1)
    expect(block!.dynamicChildren![0].dynamicChildren!.length).toBe(0)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<div><i></i></div>',
    )
  })

  test('PatchFlags: PatchFlags.TEXT', async () => {
    renderWithBlock(() => [createVNode('p', null, 'foo', PatchFlags.TEXT)])

    expect(inner(root)).toBe('<div><p>foo</p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p>foo</p>',
    )

    renderWithBlock(() => [createVNode('p', null, 'bar', PatchFlags.TEXT)])

    expect(inner(root)).toBe('<div><p>bar</p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p>bar</p>',
    )
  })

  test('PatchFlags: PatchFlags.CLASS', async () => {
    renderWithBlock(() => [
      createVNode('p', { class: 'foo' }, '', PatchFlags.CLASS),
    ])

    expect(inner(root)).toBe('<div><p class="foo"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p class="foo"></p>',
    )

    renderWithBlock(() => [
      createVNode('p', { class: 'bar' }, '', PatchFlags.CLASS),
    ])

    expect(inner(root)).toBe('<div><p class="bar"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p class="bar"></p>',
    )
  })

  test('PatchFlags: PatchFlags.STYLE', async () => {
    renderWithBlock(() => [
      createVNode('p', { style: 'color: red' }, '', PatchFlags.STYLE),
    ])

    expect(inner(root)).toBe('<div><p style="color: red"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p style="color: red"></p>',
    )

    renderWithBlock(() => [
      createVNode('p', { style: 'color: green' }, '', PatchFlags.STYLE),
    ])

    expect(inner(root)).toBe('<div><p style="color: green"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p style="color: green"></p>',
    )
  })

  test('PatchFlags: PatchFlags.PROPS', async () => {
    renderWithBlock(() => [
      createVNode('p', { id: 'foo' }, '', PatchFlags.PROPS, ['id']),
    ])

    expect(inner(root)).toBe('<div><p id="foo"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p id="foo"></p>',
    )

    renderWithBlock(() => [
      createVNode('p', { id: 'bar' }, '', PatchFlags.PROPS, ['id']),
    ])

    expect(inner(root)).toBe('<div><p id="bar"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p id="bar"></p>',
    )
  })

  test('PatchFlags: PatchFlags.FULL_PROPS', async () => {
    let propName = 'foo'

    renderWithBlock(() => [
      createVNode('p', { [propName]: 'dynamic' }, '', PatchFlags.FULL_PROPS),
    ])

    expect(inner(root)).toBe('<div><p foo="dynamic"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p foo="dynamic"></p>',
    )

    propName = 'bar'
    renderWithBlock(() => [
      createVNode('p', { [propName]: 'dynamic' }, '', PatchFlags.FULL_PROPS),
    ])

    expect(inner(root)).toBe('<div><p bar="dynamic"></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p bar="dynamic"></p>',
    )
  })

  // the order and length of the list will not change
  test('PatchFlags: PatchFlags.STABLE_FRAGMENT', async () => {
    let list = ['foo', 'bar']
    render(
      (openBlock(),
      (block = createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode('p', null, item, PatchFlags.TEXT)
        }),
        PatchFlags.STABLE_FRAGMENT,
      ))),
      root,
    )

    expect(inner(root)).toBe('<p>foo</p><p>bar</p>')
    expect(block.dynamicChildren!.length).toBe(2)
    expect(serialize(block.dynamicChildren![0].el as TestElement)).toBe(
      '<p>foo</p>',
    )
    expect(serialize(block.dynamicChildren![1].el as TestElement)).toBe(
      '<p>bar</p>',
    )

    list = list.map(item => item.repeat(2))
    render(
      (openBlock(),
      createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode('p', null, item, PatchFlags.TEXT)
        }),
        PatchFlags.STABLE_FRAGMENT,
      )),
      root,
    )

    expect(inner(root)).toBe('<p>foofoo</p><p>barbar</p>')
    expect(block.dynamicChildren!.length).toBe(2)
    expect(serialize(block.dynamicChildren![0].el as TestElement)).toBe(
      '<p>foofoo</p>',
    )
    expect(serialize(block.dynamicChildren![1].el as TestElement)).toBe(
      '<p>barbar</p>',
    )
  })

  // A Fragment with `UNKEYED_FRAGMENT` flag will always patch its children,
  // so there's no need for tracking dynamicChildren.
  test('PatchFlags: PatchFlags.UNKEYED_FRAGMENT', async () => {
    const list = [{ tag: 'p', text: 'foo' }]
    render(
      (openBlock(true),
      (block = createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode(item.tag, null, item.text)
        }),
        PatchFlags.UNKEYED_FRAGMENT,
      ))),
      root,
    )

    expect(inner(root)).toBe('<p>foo</p>')
    expect(block.dynamicChildren!.length).toBe(0)

    list.unshift({ tag: 'i', text: 'bar' })
    render(
      (openBlock(true),
      createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode(item.tag, null, item.text)
        }),
        PatchFlags.UNKEYED_FRAGMENT,
      )),
      root,
    )

    expect(inner(root)).toBe('<i>bar</i><p>foo</p>')
    expect(block.dynamicChildren!.length).toBe(0)
  })

  // A Fragment with `KEYED_FRAGMENT` will always patch its children,
  // so there's no need for tracking dynamicChildren.
  test('PatchFlags: PatchFlags.KEYED_FRAGMENT', async () => {
    const list = [{ tag: 'p', text: 'foo' }]
    render(
      (openBlock(true),
      (block = createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode(item.tag, { key: item.tag }, item.text)
        }),
        PatchFlags.KEYED_FRAGMENT,
      ))),
      root,
    )

    expect(inner(root)).toBe('<p>foo</p>')
    expect(block.dynamicChildren!.length).toBe(0)

    list.unshift({ tag: 'i', text: 'bar' })
    render(
      (openBlock(true),
      createBlock(
        Fragment,
        null,
        list.map(item => {
          return createVNode(item.tag, { key: item.tag }, item.text)
        }),
        PatchFlags.KEYED_FRAGMENT,
      )),
      root,
    )

    expect(inner(root)).toBe('<i>bar</i><p>foo</p>')
    expect(block.dynamicChildren!.length).toBe(0)
  })

  test('PatchFlags: PatchFlags.NEED_PATCH', async () => {
    const spyMounted = vi.fn()
    const spyUpdated = vi.fn()
    const count = ref(0)
    const Comp = {
      setup() {
        return () => {
          count.value
          return (
            openBlock(),
            (block = createBlock('div', null, [
              createVNode(
                'p',
                { onVnodeMounted: spyMounted, onVnodeBeforeUpdate: spyUpdated },
                '',
                PatchFlags.NEED_PATCH,
              ),
            ]))
          )
        }
      },
    }

    render(h(Comp), root)

    expect(inner(root)).toBe('<div><p></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p></p>',
    )
    expect(spyMounted).toHaveBeenCalledTimes(1)
    expect(spyUpdated).toHaveBeenCalledTimes(0)

    count.value++
    await nextTick()

    expect(inner(root)).toBe('<div><p></p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(serialize(block!.dynamicChildren![0].el as TestElement)).toBe(
      '<p></p>',
    )
    expect(spyMounted).toHaveBeenCalledTimes(1)
    expect(spyUpdated).toHaveBeenCalledTimes(1)
  })

  test('PatchFlags: PatchFlags.BAIL', async () => {
    render(
      (openBlock(),
      (block = createBlock('div', null, [createVNode('p', null, 'foo')]))),
      root,
    )

    expect(inner(root)).toBe('<div><p>foo</p></div>')
    expect(block!.dynamicChildren!.length).toBe(0)

    render(
      (openBlock(),
      (block = createBlock(
        'div',
        null,
        [createVNode('i', null, 'bar')],
        PatchFlags.BAIL,
      ))),
      root,
    )

    expect(inner(root)).toBe('<div><i>bar</i></div>')
    expect(block!.dynamicChildren).toBe(null)
  })

  // #1980
  test('dynamicChildren should be tracked correctly when normalizing slots to plain children', async () => {
    let block: VNode
    const Comp = defineComponent({
      setup(_props, { slots }) {
        return () => {
          const vnode =
            (openBlock(),
            (block = createBlock('div', null, {
              default: withCtx(() => [renderSlot(slots, 'default')]),
              _: SlotFlags.FORWARDED,
            })))

          return vnode
        }
      },
    })

    const foo = ref(0)
    const App = {
      setup() {
        return () => {
          return createBlock(Comp, null, {
            default: withCtx(() => [
              createVNode('p', null, foo.value, PatchFlags.TEXT),
            ]),
            // Indicates that this is a stable slot to avoid bail out
            _: SlotFlags.STABLE,
          })
        }
      },
    }

    render(h(App), root)
    expect(inner(root)).toBe('<div><p>0</p></div>')
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(block!.dynamicChildren![0].type).toBe(Fragment)
    expect(block!.dynamicChildren![0].dynamicChildren!.length).toBe(1)
    expect(
      serialize(
        block!.dynamicChildren![0].dynamicChildren![0].el as TestElement,
      ),
    ).toBe('<p>0</p>')

    foo.value++
    await nextTick()

    expect(inner(root)).toBe('<div><p>1</p></div>')
  })

  // #2169
  // block
  // - dynamic child (1)
  //   - component (2)
  // When unmounting (1), we know we are in optimized mode so no need to further
  // traverse unmount its children
  test('should not perform unnecessary unmount traversals', () => {
    const spy = vi.fn()
    const Child = {
      setup() {
        onBeforeUnmount(spy)
        return () => 'child'
      },
    }
    const Parent = () => (
      openBlock(),
      createBlock('div', null, [
        createVNode('div', { style: {} }, [createVNode(Child)], 4 /* STYLE */),
      ])
    )
    render(h(Parent), root)
    render(null, root)
    expect(spy).toHaveBeenCalledTimes(1)
  })

  test('should call onUnmounted hook for dynamic components receiving an existing vnode w/ component children', async () => {
    const spy = vi.fn()
    const show = ref(1)
    const Child = {
      setup() {
        onUnmounted(spy)
        return () => 'child'
      },
    }
    const foo = h('div', null, h(Child))
    const app = createApp({
      render() {
        return show.value
          ? (openBlock(),
            createBlock('div', null, [(openBlock(), createBlock(foo))]))
          : createCommentVNode('v-if', true)
      },
    })

    app.mount(root)
    show.value = 0
    await nextTick()

    expect(spy).toHaveBeenCalledTimes(1)
  })

  // #2444
  // `KEYED_FRAGMENT` and `UNKEYED_FRAGMENT` always need to diff its children
  test('non-stable Fragment always need to diff its children', () => {
    const spyA = vi.fn()
    const spyB = vi.fn()
    const ChildA = {
      setup() {
        onBeforeUnmount(spyA)
        return () => 'child'
      },
    }
    const ChildB = {
      setup() {
        onBeforeUnmount(spyB)
        return () => 'child'
      },
    }
    const Parent = () => (
      openBlock(),
      createBlock('div', null, [
        (openBlock(true),
        createBlock(
          Fragment,
          null,
          [createVNode(ChildA, { key: 0 })],
          128 /* KEYED_FRAGMENT */,
        )),
        (openBlock(true),
        createBlock(
          Fragment,
          null,
          [createVNode(ChildB)],
          256 /* UNKEYED_FRAGMENT */,
        )),
      ])
    )
    render(h(Parent), root)
    render(null, root)
    expect(spyA).toHaveBeenCalledTimes(1)
    expect(spyB).toHaveBeenCalledTimes(1)
  })

  // #2893
  test('manually rendering the optimized slots should allow subsequent updates to exit the optimized mode correctly', async () => {
    const state = ref(0)

    const CompA = {
      name: 'A',
      setup(props: any, { slots }: SetupContext) {
        return () => {
          return (
            openBlock(),
            createBlock('div', null, [renderSlot(slots, 'default')])
          )
        }
      },
    }

    const Wrapper = {
      name: 'Wrapper',
      setup(props: any, { slots }: SetupContext) {
        // use the manually written render function to rendering the optimized slots,
        // which should make subsequent updates exit the optimized mode correctly
        return () => {
          return slots.default!()[state.value]
        }
      },
    }

    const app = createApp({
      name: 'App',
      setup() {
        return () => {
          return (
            openBlock(),
            createBlock(Wrapper, null, {
              default: withCtx(() => [
                createVNode(CompA, null, {
                  default: withCtx(() => [createTextVNode('Hello')]),
                  _: 1 /* STABLE */,
                }),
                createVNode(CompA, null, {
                  default: withCtx(() => [createTextVNode('World')]),
                  _: 1 /* STABLE */,
                }),
              ]),
              _: 1 /* STABLE */,
            })
          )
        }
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<div>Hello</div>')

    state.value = 1
    await nextTick()
    expect(inner(root)).toBe('<div>World</div>')
  })

  //#3623
  test('nested teleport unmount need exit the optimization mode', () => {
    const target = nodeOps.createElement('div')
    const root = nodeOps.createElement('div')

    render(
      (openBlock(),
      createBlock('div', null, [
        (openBlock(),
        createBlock(
          Teleport as any,
          {
            to: target,
          },
          [
            createVNode('div', null, [
              (openBlock(),
              createBlock(
                Teleport as any,
                {
                  to: target,
                },
                [createVNode('div', null, 'foo')],
              )),
            ]),
          ],
        )),
      ])),
      root,
    )
    expect(inner(target)).toMatchInlineSnapshot(
      `"<div><!--teleport start--><!--teleport end--></div><div>foo</div>"`,
    )
    expect(inner(root)).toMatchInlineSnapshot(
      `"<div><!--teleport start--><!--teleport end--></div>"`,
    )

    render(null, root)
    expect(inner(target)).toBe('')
  })

  // #3548
  test('should not track dynamic children when the user calls a compiled slot inside template expression', () => {
    const Comp = {
      setup(props: any, { slots }: SetupContext) {
        return () => {
          return (
            openBlock(),
            (block = createBlock('section', null, [
              renderSlot(slots, 'default'),
            ]))
          )
        }
      },
    }

    let dynamicVNode: VNode
    const Wrapper = {
      setup(props: any, { slots }: SetupContext) {
        return () => {
          return (
            openBlock(),
            createBlock(Comp, null, {
              default: withCtx(() => {
                return [
                  (dynamicVNode = createVNode(
                    'div',
                    {
                      class: {
                        foo: !!slots.default!(),
                      },
                    },
                    null,
                    PatchFlags.CLASS,
                  )),
                ]
              }),
              _: 1,
            })
          )
        }
      },
    }
    const app = createApp({
      render() {
        return (
          openBlock(),
          createBlock(Wrapper, null, {
            default: withCtx(() => {
              return [createVNode({}) /* component */]
            }),
            _: 1,
          })
        )
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<section><div class="foo"></div></section>')
    /**
     * Block Tree:
     *  - block(div)
     *   - block(Fragment): renderSlots()
     *    - dynamicVNode
     */
    expect(block!.dynamicChildren!.length).toBe(1)
    expect(block!.dynamicChildren![0].dynamicChildren!.length).toBe(1)
    expect(block!.dynamicChildren![0].dynamicChildren![0]).toEqual(
      dynamicVNode!,
    )
  })

  // 3569
  test('should force bailout when the user manually calls the slot function', async () => {
    const index = ref(0)
    const Foo = {
      setup(props: any, { slots }: SetupContext) {
        return () => {
          return slots.default!()[index.value]
        }
      },
    }

    const app = createApp({
      setup() {
        return () => {
          return (
            openBlock(),
            createBlock(Foo, null, {
              default: withCtx(() => [
                true
                  ? (openBlock(), createBlock('p', { key: 0 }, '1'))
                  : createCommentVNode('v-if', true),
                true
                  ? (openBlock(), createBlock('p', { key: 0 }, '2'))
                  : createCommentVNode('v-if', true),
              ]),
              _: 1 /* STABLE */,
            })
          )
        }
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<p>1</p>')

    index.value = 1
    await nextTick()
    expect(inner(root)).toBe('<p>2</p>')

    index.value = 0
    await nextTick()
    expect(inner(root)).toBe('<p>1</p>')
  })

  // #3779
  test('treat slots manually written by the user as dynamic', async () => {
    const Middle = {
      setup(props: any, { slots }: any) {
        return slots.default!
      },
    }

    const Comp = {
      setup(props: any, { slots }: any) {
        return () => {
          return (
            openBlock(),
            createBlock('div', null, [
              createVNode(Middle, null, {
                default: withCtx(
                  () => [
                    createVNode('div', null, [renderSlot(slots, 'default')]),
                  ],
                  undefined,
                ),
                _: 3 /* FORWARDED */,
              }),
            ])
          )
        }
      },
    }

    const loading = ref(false)
    const app = createApp({
      setup() {
        return () => {
          // important: write the slot content here
          const content = h('span', loading.value ? 'loading' : 'loaded')
          return h(Comp, null, {
            default: () => content,
          })
        }
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<div><div><span>loaded</span></div></div>')

    loading.value = true
    await nextTick()
    expect(inner(root)).toBe('<div><div><span>loading</span></div></div>')
  })

  // #3828
  test('patch Suspense in optimized mode w/ nested dynamic nodes', async () => {
    const show = ref(false)

    const app = createApp({
      render() {
        return (
          openBlock(),
          createBlock(
            Fragment,
            null,
            [
              (openBlock(),
              createBlock(SuspenseImpl, null, {
                default: withCtx(() => [
                  createVNode('div', null, [
                    createVNode('div', null, show.value, PatchFlags.TEXT),
                  ]),
                ]),
                _: SlotFlags.STABLE,
              })),
            ],
            PatchFlags.STABLE_FRAGMENT,
          )
        )
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<div><div>false</div></div>')

    show.value = true
    await nextTick()
    expect(inner(root)).toBe('<div><div>true</div></div>')
  })

  // #4183
  test('should not take unmount children fast path /w Suspense', async () => {
    const show = ref(true)
    const spyUnmounted = vi.fn()

    const Parent = {
      setup(props: any, { slots }: SetupContext) {
        return () => (
          openBlock(),
          createBlock(SuspenseImpl, null, {
            default: withCtx(() => [renderSlot(slots, 'default')]),
            _: SlotFlags.FORWARDED,
          })
        )
      },
    }

    const Child = {
      setup() {
        onUnmounted(spyUnmounted)
        return () => createVNode('div', null, show.value, PatchFlags.TEXT)
      },
    }

    const app = createApp({
      render() {
        return show.value
          ? (openBlock(),
            createBlock(
              Parent,
              { key: 0 },
              {
                default: withCtx(() => [createVNode(Child)]),
                _: SlotFlags.STABLE,
              },
            ))
          : createCommentVNode('v-if', true)
      },
    })

    app.mount(root)
    expect(inner(root)).toBe('<div>true</div>')

    show.value = false
    await nextTick()
    expect(inner(root)).toBe('<!--v-if-->')
    expect(spyUnmounted).toHaveBeenCalledTimes(1)
  })

  // #3881
  // root cause: fragment inside a compiled slot passed to component which
  // programmatically invokes the slot. The entire slot should de-opt but
  // the fragment was incorrectly put in optimized mode which causes it to skip
  // updates for its inner components.
  test('fragments inside programmatically invoked compiled slot should de-opt properly', async () => {
    const Parent: FunctionalComponent = (_, { slots }) => slots.default!()
    const Dummy = () => 'dummy'

    const toggle = ref(true)
    const force = ref(0)

    const app = createApp({
      render() {
        if (!toggle.value) {
          return null
        }
        return h(
          Parent,
          { n: force.value },
          {
            default: withCtx(
              () => [
                createVNode('ul', null, [
                  (openBlock(),
                  createBlock(
                    Fragment,
                    null,
                    renderList(1, item => {
                      return createVNode('li', null, [createVNode(Dummy)])
                    }),
                    64 /* STABLE_FRAGMENT */,
                  )),
                ]),
              ],
              undefined,
              true,
            ),
            _: 1 /* STABLE */,
          },
        )
      },
    })

    app.mount(root)

    // force a patch
    force.value++
    await nextTick()
    expect(inner(root)).toBe(`<ul><li>dummy</li></ul>`)

    // unmount
    toggle.value = false
    await nextTick()
    // should successfully unmount without error
    expect(inner(root)).toBe(`<!---->`)
  })
})